Physiological analysis of methods to relieve dormancy of lettuce seeds

R. Weges

Research output: Thesisinternal PhD, WU

Abstract

<p>Low maximum temperature of germination restricts the cultivation of a number of lettuce cultivars to temperate conditions. Pretreatments have been studied that increase the maximum germination temperature, which is characterized by the temperature for 50% germination (T <sub><font size="-1">50</font></sub> ). Pretreatment consists of pre-incubation, redesiccation and storage. Pre- incubation during 16 to 20 h at 15 °C in water increases T <sub><font size="-1">50</font></sub> with 4 to 10 °C, depending on cultivar. Redesiccation does not cause visible damage to seeds, as judged from the developing seedling, provided that germination has not started during pre-incubation. In cultivars with a high original T <sub><font size="-1">50</font></sub> redesiccation does not affect T <sub><font size="-1">50</font></sub> . However, if the original T <sub><font size="-1">50</font></sub> is low, redesiccation causes a drop of T <sub><font size="-1">50</font></sub> to values close to the original T <sub><font size="-1">50</font></sub> value. The effect of redesiccation is mainly determined by the final moisture content. Temperature and rate of drying are of minor importance in this respect. Pre-incubation in solutions of polyethylene glycol makes the seeds desiccation tolerant. Dehydration results in increased K <sup><font size="-1">+</font></SUP>leakage from isolated embryos, in contrast to intact seeds that do not leak due to K <sup><font size="-1">+</font></SUP>-impermeable endosperm cells. T <sub><font size="-1">50</font></sub> decreases during storage. The decrease of T <sub><font size="-1">50</font></sub> and the loss of seed viability show a similar positive relationship to temperature and moisture content during storage. Besides the rise of T <sub><font size="-1">50</font></sub> , pre-incubation at 15 °C also enhances the capacity of seeds to germinate at increasingly more negative osmotic potentials of the incubation medium (Ψπe). The effect is characterized by the minimal Ψπe of the incubation medium for 50% germination (Ψ <sub><font size="-1">50</font></sub> ). Pre-incubation at 30 °C has an opposite effect. The change of Ψ <sub><font size="-1">50</font></sub> does not correspond with a change in concentration of amino nitrogen compounds. Both actual water potential (Ψ) and osmotic potential (Ψπ), as determined with a psychrometer, are not correlated with changing Ψ <sub><font size="-1">50</font></sub> values. Calculations based on the general equation of hydraulic cell growth indicate that changes in T <sub><font size="-1">50</font></sub> are correlated with parallel changes in the yield threshold (Y) of turgor pressure. Changes in Y appear to occur mainly in the seed envelope.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
Supervisors/Advisors
  • Karssen, C.M., Promotor
Award date28 Jan 1987
Place of PublicationS.l.
Publisher
Publication statusPublished - 1987

Keywords

  • seeds
  • stratification
  • lactuca sativa
  • lettuces
  • germination
  • seed germination
  • seed dormancy

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